Toggle locking gripping tools come in the form of pliers, wrenches, clamps, bar clamps, tongs and many other hand-held clamping and crimping tools. One example of one of the most widely recognized types are pliers known by the trademark name Vise-Grip®.
These tools have a jaw fixed to a stationary handle, a movable jaw connected to a moving handle with a toggle link member connecting both the moving handle at a toggle pivot and the fixed handle. Typically, but not always, there is a means to adjust the opening space between the two jaws by moving the toggle link connection in relation to the fixed jaw. These means can consist of an adjustment screw or other means in the fixed handle or more recently “auto adjusting” type tools such as U.S. Pat. No. 6,708,588 to (Kesinger et al. 2004) that use cams, lock washers and the like that automatically clamp at a set force without needing any manual jaw opening adjustment.
Operation of these types of tools is simple; the operator squeezes the moving handle towards the fixed handle. This causes the two jaws to grip the work-piece and simultaneously causes the moving handle and toggle link to rotate inwards towards the fixed handle. As a result the toggle pivot moves just past what is commonly referred to as toggle over center line (also referred to as over center lock or past dead center) which is a reference line between the attachment of the moving handle to moving jaw and the attachment of the toggle link to the fixed handle body. This results in the tool positively gripping the work-piece with forces that can be enormous (this is often referred to as the jaws being locked, jaws toggle locked or toggle lock).
Many solutions to the problem of releasing the jaws when locked have been tried and all have disadvantages.
When toggle lock tools first started coming on to the market, the only way to release the force was to pry the two handles apart. This required the user to have to use both hands to accomplish this and the outwards release of great force could injure the user and/or damage the work-piece.
Later versions incorporated a release lever in the moving handle that projected out past the end of the moving handle. Moving this handle resulted in it contacting either the toggle link or fixed handle body, resulting in the moving handle moving outwards, the toggle pivot moving back over the toggle over center line and the jaws being unlocked. Once again, operation of this lever required the user to either shift their hand on the tool or use both hands. In addition, the user could only use the force of one or two fingers, which were often pinched by the release lever and handles.
Some inventions such as U.S. Pat. No. 8,225,700 (Hile, 2012) tried to solve the release problem by having a releasable ‘fixed’ jaw with a thumb release on the fixed handle. Apart from the added mechanical complexity and cost, there are ergonomic issues such as limited gripping area on the fixed handle and the potential for accidental release from hitting the thumb release when using the tool.
More recently some toggle lock pliers have been marketed using an outwards release method involving an extra link between the toggle link and moving handle. This gives the invention added mechanical advantage but does not change the fact that two hands are still needed to pry the two levers apart, nor does it address the issue of the violent release of outwards force. U.S. Pat. No. 2,838,973 (Peterson, 1958) and U.S. Pat. No. 7,454,999 (Wu, 2008) are two such examples of this type of toggle lock pliers.
There have been a few attempts at creating a release method using a moving segmented handle and having the rear section pivot inwards towards the fixed handle to release the toggle lock, all of which have serious shortcomings.
U.S. Pat. No. 2,532,659 (Burns, 1950) uses a segmented handle that has a rear segment called a releasing handle pivoting inwards to release the toggle lock. In this design, the releasing handle latches directly onto the toggle linkage (‘Toggle linkage’ in this patent is the definition for the front handle section) without any intermediary member. The operator releases the toggle lock by sliding the releasing handle detent means from engagement with the toggle linkage detent means. A cam projection provides a fulcrum on the releasing handle that contacts the fixed handle that causes the toggle lock to be broken when the releasing handle is rotated inwards towards the fixed handle.
This design creates two conflicting problems: Either the releasing handle is easily slid off the detent, which could result in a violent accidental release of the jaws while torqueing the pliers; or the releasing handle is stiff in relation to the detent, thus making the releasing handle difficult to easily manipulate from the detent in order to release the toggle lock. In addition, because the cam is used as a toggle pivot over center stop, it results in large outwards torque force on the release handle making disengaging the detent difficult when the jaws are locked.
U.S. Pat. No. 2,543,922 (Mead, 1951) uses a segmented handle using a rear handle section pivoting inwards towards the fixed handle to release the toggle lock. In this design, a key block acts as a release member sandwiched between the front handle section and rear handle section normally keeping the two rigid to one another with thicker key block cross section. By sliding the block sandwiched in between the front and rear handle sections, the key block cross section is moved out from between the two sections allowing some loose play, which allows the user to pivot the rear handle section inward. Pivoting the rear section inwards results in the fulcrum point part of the rear handle section coming in contact with the toggle bar, which causes the front handle section to rotate outwards and the toggle lock to be broken.
This design has multiple serious drawbacks. By sandwiching the key block between the front and rear handle sections, instead of mounting and retaining the block movably on one section or the other, the key block has the chance of falling out of the assembly altogether if the two sections are not tightly sandwiching the key block. Conversely, if the two sections do sandwich the key block tightly, the key block will be difficult to operate because of high friction.
In addition, because the rear handle section is used as a toggle pivot over center stop, it will result in large outwards torque force on the rear handle section when the jaws are locked. The resulting torque and movement of the rear handle section could force the key block out between the two sections. This would result in the front and rear sections becoming accidently uncoupled and no longer rigid to one another.
Another major issue with this design is the fact that the range of rotation of the rear handle section is limited by the presence of the key block sandwiched in between the front and rear handle sections; in some cases this could result in there not being enough inward rotation movement to break the toggle lock. Yet another problem is that the key block would constantly be getting caught on the shank of the front handle section because there is no means of guiding it into alignment.
Often confused with toggle lock pliers is another type of locking pliers such as U.S. Pat. No. 6,227,080 (Grayo et al, 2001). Although these types of locking pliers have a release trigger on the moving handle, they do not use an over toggle locking design, but instead use a catch to engage and stop the toggle pivot just short of passing over the toggle over center line. The toggle lock is released by triggering this catch. This type of locking plier design has several problems such as the added mechanical complexity resulting in increased cost and reduced reliability. The catch is subject to a large force over a small area and can wear rapidly, and at higher force settings it can be difficult to get the catch to engage at all.